Re: [RFC PATCH v15 4/7] sched: Fix runtime accounting w/ split exec & sched contexts

Steven Rostedt
2025-03-13T10:26:15Z

On Wed, 12 Mar 2025 15:11:34 -0700
John Stultz <jstultz@google.com> wrote:

> The idea here is we want to charge the scheduler-context task's
> vruntime but charge the execution-context task's sum_exec_runtime.

The "but" is confusing me. Do you mean, "and also"? The sentence
doesn't make sense with "but" unless it was:

"The idea here is we DON'T want to charge the scheduler-context
task's vruntime but charge the execution-context task's
sum_exec_runtime INSTEAD."

>
> This way cputime accounting goes against the task actually running
> but vruntime accounting goes against the rq->donor task so we get
> proper fairness.

But this shows that you want to do both, although, I would remove the
"but" here too. Replace it with "while".

Or maybe I'm just confused.

> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index c798d27952431..f8ad3a44b3771 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1129,22 +1129,33 @@ static void update_tg_load_avg(struct cfs_rq *cfs_rq)
> }
> #endif /* CONFIG_SMP */
>
> -static s64 update_curr_se(struct rq *rq, struct sched_entity *curr)
> +static s64 update_curr_se(struct rq *rq, struct sched_entity *se)

Should this be renamed to "update_se()" as it no longer appears to be
updating "curr_se".

> {
> u64 now = rq_clock_task(rq);
> s64 delta_exec;
>
> - delta_exec = now - curr->exec_start;
> + delta_exec = now - se->exec_start;
> if (unlikely(delta_exec <= 0))
> return delta_exec;
>
> - curr->exec_start = now;
> - curr->sum_exec_runtime += delta_exec;
> + se->exec_start = now;
> + if (entity_is_task(se)) {
> + struct task_struct *running = rq->curr;
> + /*
> + * If se is a task, we account the time against the running
> + * task, as w/ proxy-exec they may not be the same.
> + */
> + running->se.exec_start = now;
> + running->se.sum_exec_runtime += delta_exec;
> + } else {
> + /* If not task, account the time against se */
> + se->sum_exec_runtime += delta_exec;
> + }

Or maybe: update_proxy_se() ?

-- Steve

>
> if (schedstat_enabled()) {
> struct sched_statistics *stats;
>
> - stats = __schedstats_from_se(curr);
> + stats = __schedstats_from_se(se);
> __schedstat_set(stats->exec_max,
> max(delta_exec, stats->exec_max));
> }